Hydraulic torque converters, devices used to change the ratio of torque to speed between the input and output shafts of the converter, revolutionized the automotive and marine propulsion industries by providing hydraulic means to transfer energy from an engine to a drive mechanism, e.g., drive shaft or automatic transmission, while smoothing out engine power pulses. A torque converter, arranged between the engine and the transmission, includes three primary components: an impeller, sometimes referred to as a pump, directly connected to the converter's cover and thereby the engine's crankshaft; a turbine, similar in structure to the impeller, however the turbine is connected to the input shaft of the transmission; and, a stator, located between the impeller and turbine, which redirects the flow of hydraulic fluid exiting from the turbine thereby providing additional rotational force to the pump.
FIG. 1 is a cross sectional view of prior art torque converter 10 arranged between engine crankshaft 12 and transmission 14. As shown in FIG. 2, torque converters typically are enclosed by a two piece cover, i.e., front and back covers 16 and 18, respectively. Engine crankshaft 12 includes flexplate 20 fixedly secured thereto via bolts 22. Front cover 16 faces engine crankshaft 12 and is fixedly secured thereto via bolts 24, while back cover 18, which includes impeller 26, is proximate transmission 14 and fixedly secured to front cover 16 via weld 28. As can be seen in FIG. 1, in addition to bolts 24, front cover 16 often includes pilot boss 30 which helps align and hold torque converter 10 to engine crankshaft 12.
A variety of methods of incorporating a pilot boss are known in the art. For example, U.S. Pat. No. 6,474,062 issued on Nov. 5, 2002 to Yamanaka et al. teaches a method of producing a pilot boss by forming a torque converter cover with plastic working operations, e.g., stamping and rolling. Additionally, Yamanaka et al. describe an alternative method of incorporating a pilot boss in a torque converter, i.e., welding a flanged pilot within a through hole in the front cover. Other methods include welding a pilot to the front surface of the front cover. For example, as shown in FIG. 1, pilot boss 30 is fixedly secured to front cover 16 via weld 32. At times, when a pilot boss is formed via welding or stamping, secondary turning operations are necessary to correct for variability in manufacturing processes. In other words, a fully assembled torque converter cover must be corrected to meet required tolerances.
Thus, there is a long-felt need for a low cost means for and method of affixing a pilot boss to a torque converter cover. There also is a long-felt need for a simplified method of affixing a pilot boss to a torque converter cover which maintains tolerances and does not require secondary finishing operations after the cover with pilot boss is formed.